Electrically conductive floor covering

ABSTRACT

An electrically conductive floor covering made of first particles of a polymer material which are surrounded with electrically conductive second particles and compressed in the intermediate space between the top and bottom sides of the floor covering, with the floor covering having at least one cut surface and the electrically conductive second particles forming conductive paths which connect the upper side and the lower side of the floor covering in an electrically conductive way, in which the first particles comprise at least one granulated elastomer material and form a matrix, in which the second particles form electric conductive paths along the particle boundaries of the first particles.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an electrically conductive floorcovering.

[0003] 2. Description of Related Art

[0004] Static charges which are produced by walking or traveling onplastic floor coverings, particularly at low atmospheric humidity,represent a serious problem, particularly for sensitive electroniccomponents. The electronic components may be damaged or their functionmay be impaired by electrostatic discharges. Furthermore, in areas inwhich easily flammable materials are worked with, there is the dangerthat these materials will be ignited by spark-over in the event ofstatic discharges. The avoidance of static charges is particularlyimportant in surroundings which are air-conditioned and therefore have alow atmospheric humidity, such as computer centers, manufacturingfacilities for electronic components and electronic devices,radiological facilities, operating rooms, and other areas in which careis taken to provide an atmosphere low in dust and particles.

[0005] The floor coverings typically used, for example those based onpolyvinyl chloride or rubber mixtures, are insulators. They may be madeconductive if conductive fillers or antistatic agents are mixed in.However, a relatively large quantity, typically between 30 and 50volume-percent of a conductive filler, must be used to achieve asufficient conductivity. Metallic materials, conductive carbon black, orgraphite are used in particular as conductive fillers, but the use ofthe necessary quantities results in black or gray products. Ifantistatic agents are used, there is the disadvantage that thesematerials react very strongly to changes in atmospheric humidity andtheir effectiveness is therefore strongly dependent on the environmentalconditions.

[0006] A method for producing highly compressed, conductive coveringmaterial from thermoplastic plastics is known from European Patent A 869217, in which particles of the thermoplastic plastic, which are providedwith a coating containing a conductive substance, are compressed underelevated temperature and high pressure into a block with conductivepaths and subsequently split transversely to the direction of theconductive paths into slabs of the desired thickness, with these slabshaving conductive paths in the direction of their thickness. In thisway, light-colored, conductive floor coverings made of thermoplasticplastic are obtained.

SUMMARY OF THE INVENTION

[0007] It is an object of the invention to provide an electricallyconductive floor covering which contains a maximum of 3 weight-percentof conductive substances.

[0008] These and other objects of the invention are achieved by anelectrically conductive floor covering in which the first particlescomprise at least one granulated elastomer material and form a matrix inwhich the second particles form electrically conductive paths along theparticle boundaries of the first particles.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The floor covering according to the invention allows theproduction of floor coverings with an irregular pattern, which has theconductive paths cut during production. The electrically conductiveelastomer floor covering according to the present invention has anelectric volume resistance measured according to IEC 61340 in the rangefrom 10⁵ to 10⁷ Ω. Furthermore, the electrically conductive elastomerfloor covering according to the present invention features a surfacequality which corresponds to electrically non-conductive elastomer floorcoverings.

[0010] The electrically conductive elastomer floor covering ispreferably one in which the granulated particles pass through sieveswith a mesh size between 2 to 8 mm. The conductivity of the finalproduct can be set via the size of the granulated particles and thus bythe number of conductive paths per unit area.

[0011] The electrically conductive elastomer floor covering containssubstances such as carbon black, graphite, metal powder, or conductivelydoped mineral materials with a grain size <15 μm as the electricallyconductive second particles.

[0012] An electrically conductive elastomer floor covering whichcontains conductive doped mineral fillers such as mica coated withantimony-doped tin oxide is particularly preferred. This embodimentallows the formation of colored conductive paths depending on thepigmentation, in contrast to the black conductive paths if carbon blackor graphite is used.

[0013] An electrically conductive elastomer floor covering whichcontains 0.05 to 0.8 weight-percent of the electrically conductivesecond particles is particularly preferred. In spite of this very lowcontent of conductive substances, electrically conductive elastomerfloor coverings are thus obtained which have an electrical volumeresistance in the range desired by the user.

[0014] Therefore, electrically conductive elastomer floor coverings arepossible, having black conductive paths if carbon black or graphite isused or having colored conductive paths if coated mica is used, as aredark colored elastomer floor coverings, in which the conductive pathsare set off by color for optical reasons through the use of the coatedmica and appropriate pigments.

[0015] The electrically conductive elastomer floor covering according tothe present invention is produced in that

[0016] a) one or more unvulcanized elastomer mixtures are granulated,

[0017] b) granulated particles which pass through sieves having a meshwidth of 2 to 8 mm are coated with conductive substances,

[0018] c) put in a mold and compressed and cross-linked in a firstcompression procedure at a specific pressure of 5 to 200 bar and atemperature of 60° to 120° C.,

[0019] d) split into strips or slabs, and

[0020] e) vulcanized in a second compression procedure.

[0021] The method according to the present invention allows theproduction of electrically conductive elastomer floor coverings whosesurface properties are comparable with those of electricallynon-conductive elastomer floor coverings.

[0022] The production of the electrically conductive elastomer floorcovering preferably occurs in such a way that the conductive substancesare tumbled onto the granulated particles. This method allows effectivecovering of the granulated particles with conductive substances, throughwhich the conductivity of the final product required by the user isachieved with a low use of conductive substances.

[0023] The conductive substances are preferably applied in the form of abonding agent dispersion. In this way, problems with dust can be avoidedand, the mechanical strength properties of the final product can beimproved. In particular, an aqueous latex bonding agent is preferablyused for this purpose. The use of a latex bonding agent reduces theoutlay for safety arrangements and the corresponding environmentalimpacts because organic solvents are not used.

[0024] Multicolored, patterned, or wedge-shaped striped granulatedparticles are advantageously used in statistically uniform distribution.In particular light-colored granulated particles are preferably used inthis case.

[0025] The vulcanization in the second compression procedureadvantageously occurs at a temperature of 150° to 190° C. and a specificpressure of 100 to 250 bar for a period of 2 to 10 minutes. Thevulcanization performed under these conditions results in a finalproduct whose surface properties are comparable with those of typicalnon-conductive elastomer floor coverings.

[0026] The present invention will be described in more detail in thefollowing with reference to two examples and a comparative example.

EXAMPLE 1

[0027] A screw-type short extruder is charged with a raw rubber mixture.The extruder is provided with a perforated disk through which the rawrubber mass is pressed and granulated by chopping off the strands. Thegranulate obtained is coated with an electrically conductive substanceby tumbling and subsequently placed in a mold corresponding to the sizeof the final product, but two or more times thicker, with the quantityof granulate being tailored to the volume of the form with a smallexcess of approximately 5%, and compressed at a temperature of 80° C.and a pressure of approximately 100 bar for 0.5 min./mm of finalthickness. Subsequently, the material is removed from the mold, split tothe desired final thickness by means of a splitting procedure, andcompressed and vulcanized into the final product in a second compressionprocedure at a temperature of approximately 180° C. and a pressure ofapproximately 200 bar for 4 minutes at a final thickness of 2 mm in anappropriately thick mold having a smooth or lightly structured surface.The surface of the electrically conductive elastomer floor coveringobtained in this way has few pores and is free of splitting marks.

COMPARATIVE EXAMPLE

[0028] A raw rubber mixture granulated and coated in accordance withExample 1 is compressed at a temperature of 180° C. and a pressure ofapproximately 200 bar and completely vulcanized. The splitting of theslab to the final thickness dimension results in products with a surfacehaving splitting marks and other surface faults, such as pores. Thesesurface faults allow increased soiling during use as a floor covering.

EXAMPLE 2

[0029] A carbon black-latex mixture is added to granulates made of a rawrubber mixture, which is produced by pulverizing a rough sheet in agranulating machine at room temperature and limiting the grain size viaa sieve insert of, for example, 15 mm hole width. In this case, 50 g ofthe carbon black-latex mixture is used for each 1000 g of granulate. Thelatex mixture contains 32.9 g of nitryl butadiene rubber (NBR) latexeswith a solids content of 47.5 weight-percent, 15.6 g of a 25weight-percent dispersion of an electrically conductive carbon black inwater, and 1.5 grams of a mixture containing cross-linking chemicalssuch as sulfur, zinc oxide, stearic acid, and cyclohexyl benzothiazylsulfeneamide. The granulate and the carbon-black latex dispersion arecarefully mixed with one another. The mixing occurs, for example,through tumbling in a sufficiently large vessel. After mixing, thecoated granulate is dried at room temperature or temperatures up to 35°C. and then processed according to example 1 into the electricallyconductive elastomer floor covering according to the present invention.

What is claimed is:
 1. An electrically conductive floor coveringcomprising first particles of a polymer material which are surroundedwith electrically conductive second particles and compressed in theintermediate space between the top and bottom sides of the floorcovering, the floor covering having at least one cut surface and theelectrically conductive second particles forming conductive paths whichconnect the top side and the bottom side of the floor covering in anelectrically conductive way, wherein the first particles are made of atleast one granulated elastomer material and form a matrix in which thesecond particles form electrically conductive paths along the particleboundaries of the first particles.
 2. The floor covering according toclaim 1, wherein it contains 0.05 to 0.8 weight-percent of theelectrically conductive second particles.
 3. A method for producing afloor covering according to claim 1, comprising: a) granulating at leastone unvulcanized elastomer mixture, b) passing granulated particlesthrough sieves having a mesh width of 2 to 8 mm and coating thegranulated particles with electrically conductive second particles, c)molding, compressing and cross-linking the particles in a firstcompression procedure at a specific pressure of 5 to 200 bar and atemperature of 60 to 120° C., d) splitting the molded material intostrips or slabs, and e) vulcanizing the molded material in a secondcompression procedure.
 4. The method according to claim 3, wherein theelectrically conductive second particles are tumbled onto the granulatedelastomers.
 5. The method according to claim 3, wherein the electricallyconductive second particles are applied in the form of a bonding agentdispersion.
 6. The method according to claim 5, wherein an aqueous latexbonding agent is used.
 7. The method according to claim 3, whereinmulticolored, patterned, or wedge-shaped striped granulated particlesare used in statistically uniform distribution.
 8. The method accordingto claim 4, wherein multicolored, patterned, or wedge-shaped stripedgranulated particles are used in statistically uniform distribution. 9.The method according to claim 5, wherein multicolored, patterned, orwedge-shaped striped granulated particles are used in statisticallyuniform distribution.
 10. The method according to claim 3, wherein thevulcanization in the second compression procedure occurs at temperaturesof 150° to 190° C. at a specific pressure of 100 to 250 bar in a periodof 2 to 10 minutes.
 11. The method according to claim 4, wherein thevulcanization in the second compression procedure occurs at temperaturesof 150° to 190° C. at a specific pressure of 100 to 250 bar in a periodof 2 to 10 minutes.
 12. The method according to claim 5, wherein thevulcanization in the second compression procedure occurs at temperaturesof 150° to 190° C. at a specific pressure of 100 to 250 bar in a periodof 2 to 10 minutes.
 13. The method according to claim 7, wherein thevulcanization in the second compression procedure occurs at temperaturesof 150° to 190° C. at a specific pressure of 100 to 250 bar in a periodof 2 to 10 minutes.
 14. The method according to claim 3, whereinconductive substances selected from the group consisting of carbonblack, graphite, metal powder, and conductively doped mineral materialshaving a grain size <15 μm are used.
 15. The method according to claim4, wherein conductive substances selected from the group consisting ofcarbon black, graphite, metal powder, and conductively doped mineralmaterials having a grain size <15 μm are used.
 16. The method accordingto claim 5, wherein conductive substances selected from the groupconsisting of carbon black, graphite, metal powder, and conductivelydoped mineral materials having a grain size <15 μm are used.
 17. Themethod according to claim 7, wherein conductive substances selected fromthe group consisting of carbon black, graphite, metal powder, andconductively doped mineral materials having a grain size <15 μm areused.
 18. The method according to claim 10, wherein conductivesubstances selected from the group consisting of carbon black, graphite,metal powder, and conductively doped mineral materials having a grainsize <15 μm are used.
 19. The method according to claim 14, whereinconductively doped mineral fillers such as mica coated withantimony-doped tin oxide are used.
 20. The method according to claim 15,wherein conductively doped mineral fillers such as mica coated withantimony-doped tin oxide are used.